Cartilage is soft tissue with a limited capacity for regeneration. Thus, it is difficult to naturally regenerate cartilage that has been fractured or defected due to accidents, diseases, or the like. In the past, accordingly, cartilage defects used to be mainly restored by a technique referred to as “mosaicplasty,” in which cartilage tissues were harvested from a non-weight-bearing region and transplanted into the affected area. Use of a patient's own tissues, however, imposes a heavy burden on the patient, and the amounts thereof that can be obtained are limited. Accordingly, the allograft technique that utilizes cartilage tissues of another individual has been attempted as an alternative thereto. Because of the problems of immunological rejection or infection, sufficient outcomes have not yet been attained.
Research into regenerative medicine has recently been making progress. In such regenerative medicine, cells removed from a body are cultured and organized in vitro, tissues that are as similar as possible to those in the body are reconstructed, and they are used to replace tissues in the body. Since the tissues regenerated in such a technique originate from the patient, they do not cause problems such as immunological rejection or infection. Thus, this technique has drawn attention as an ideal means for restoring tissue defects. Due to the reasons as mentioned above, regeneration of cartilage tissues in vitro has been attempted by many research institutes.
Cells exist in a body by adhering to the extracellular matrix and differentiate and proliferate with the use thereof as a scaffold. In order to construct a perfect three-dimensional tissue via in vitro cell culture, accordingly, it is necessary to provide a scaffold that is suitable for cell differentiation and proliferation. Up to the present, beneficial outcomes of tissue regeneration have been attained in hard tissue regeneration with the use of collagen, agarose, or other types of gel for a scaffold.
Even when the regenerated cartilage tissues are transplanted in the body, a new issue arises. That is, cartilage defects cannot be sufficiently supplemented due to weak adhesion between the bone tissues at the transplantation site and the regenerated cartilage tissues.
Schaefer et al. reported a method for preparing hard/soft tissue interface-like tissues by constructing cartilage-like tissues with the use of a biodegradable scaffold consisting of polyglycolic acid, separately constructing bone-like tissues with the use of a scaffold consisting of a lactic acid-glycolic acid copolymer and polyethylene glycol, and then artificially bonding them (Schaefer et al., Biomaterials 21, 2000, pp. 2599-2606). Hard/soft tissue interface-like tissues (bone/cartilage interface-like tissues) prepared by such method, however, are disadvantageously insufficient in terms of forming a bond between hard tissue (bone) and soft tissue (cartilage).
In contrast, Yaylaoglu et al. reported a method for preparing a bone/cartilage implant by generating calcium phosphate in a lyophilized collagen sponge (Gelfix® membrane, Abdi-Ibrahim), and culturing cartilage cells using it as a scaffold (Yaylaglu et al., Biomaterials 20, 1999, pp. 1513-1520). A material that simply comprises calcium phosphate, however, insufficiently bonds to hard tissues (bones) and thus cannot effectively regenerate a hard/soft tissue interface (a bone/cartilage interface herein).